Lengthen eye tail vs Lengthen eye center
Lengthening eye tail can make people focus on both sides of your eyes and they can look more charming. But if the original eye distance has already been very wide, this kind will be a disaster. Lengthening eye center is more in line with eyelashes’ natural distribution, relatively natural and all-match.

Cross vs Cluster
Each of the cross eyelashes is basically left or right, not straight forward. It is more natural to wear. Cluster eyelashes are more suitable for "Bobby" sense of daily makeup.

Long vs Short
The shortest eyelash is only 4 mm long. It is usually used as bottom eyelashes, also can make dense upper eyelashes invisible. As for length, 18 mm is common and looks like a small fan. With a blink, the opposite person can go far.